Apparatus for determining the density of a direct current



Oct. 9, 1962 w, HUBER 3 ,058,056

APPARATUS FOR DETERMINING THE DENSITY OF A DIRECT CURRENT Filed May 29,1959 5" Sheets-Sheet l Oct. 9, 1962 w. HUBER 3,058,056 APPARATUS FORDETERMINING THE DENSITY OF A DIRECT CURRENT Filed May 29, 1959 3Sheets-Sheet 2 Oct. 9, 1962 W. HUBER APPARATUS FOR DETERMINING THEDENSITY OF A DIRECT CURRENT Filed May 29, 1959 3 Sheets-Sheet 3 UnitedStates Patent 3,65%,ti'5 APPARATUS DETERMHNKNG THE DENEEHTY 9F A CURRENTWiiiy Hither, iieethovenstrasse 43, Zurich, Switzerland Fiied May 29,1955, Ser. No. 816,305 Claims priority, appiicatien Switzeriand May 30,1958 21 Ciairns. (Cl. 324-29) The present invention refers to the art ofplating or electrolytically oxidizing. More specifically, the inventionconcerns an apparatus for determining the density of a direct currentflowing through an electrolyte used in this art.

If it is desired, to predetermine the thickness of an electrolyticdeposit or to predetermine the modification of a surface of an object toa certain degree during electrolytic oxidation or electrolyticpolishing, it is necessary to know the density of the current next tothe particular surface area of the object to be treated. Generally, itis not enough to calculate the average current density on the basis ofthe known amperage and the total area of the surface to be treated. Ifthe objects are not flat so that certain portions thereof havesubstantially different distances from the counter electrode, then thecurrent density varies between these difierent area portions and wherethe distance is greatest, the current density is considerably below theaverage value. If the duration of the electrolytic treatment ispredetermined on the basis of average current density, then those areapoitions which are farthest from the counter electrode obtain only aninsuflicient deposit or an insufficient surface treatment. If, forinstance, the electrolytic deposit or the electrolytic surface treatment is intended to serve as a protection against corrosion then thispurpose is not accomplished if area portions are insufficiently treated.In that case, the treatment must be continued until its effect issuflicient even at those area portions which are treated with the leastcurrent density. Consequently, the required duration of the treatmentcannot be determined without knowing the local current density at thosearea portions which are most remote from the counter electrode.

In practice, the local current density cannot be calculated on the basisof average current density and of the three-dimensional formation of thesurfaces to be treated, and such a calculation could not take intoaccount that the polarization phenomena caused by actual current densityat the electrodes in turn influenced the current density.

It is known to measure the current density by means of an amperemeterwhich e.g. in the case of cathodic treatment is connected with the anodeand a probe electrode that may consist of a metal plate of say 16 squareinches and is placed close to the desired surface area. However, withthis method, it is not possible to determine the current density if thesurface to be treated has a complicated three-dimensional formation,particularly if it has deep recesses. Also, the probe electrodeinfluences the distribution of the current and polarization phenomena atthe cathode are not taken into account, and in addition the electrolytebetween the anode and the probe electrode constitutes a conductor inparallel with the amperemeter.

It is, therefore, a main object of this invention to overcome thedeficiencies of known methods and apparatus and to provide for anapparatus permitting to determine the current density in a simple,efficient and accurate manner.

With above object in view, an apparatus according to the invention fordetermining the density of a direct current flowing through a particularportion of an electrolyte comprises, in combination, probe meansincluding a pair of probe electrodes between which a current is adaptedto flow in said electrolyte and means connected to said electrodesincluding adjustable resistor means and control means for adjusting saidadjustable resistor means in such a manner that the resistance thereofis inversely proportional to the conductance of said electrolyte betweensaid electrodes. The apparatus further comprises measuring meansconnected to said electrodes and including said adjustable resistormeans and indicator means for indicating a potential difference set upby said current flowing between said electrodes, whereby bydetermination of said potential difference after adjustment of theresistance of said adjustable resistor means by said control means, saidpotential difference will be an indication of the density of saidcurrent flowing through said electrolyte between said electrodes.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings inwhich:

FIG. 1 is a schematic circuit diagram illustrating a basic embodiment ofthe invention;

FIG. 2 is a schematic circuit diagram showing a modified embodiment ofthe invention;

FIG. 3 is a schematic circuit diagram illustrating another embodiment ofthe invention;

FIG. 4 is aschematic circuit diagram illustrating still anotherembodiment of the invention;

FIG. 5 is a schematic circuit diagram illustrating one more embodimentof the invention; and

FIG. 6 is a cross-sectional view of probe electrode means used in anyone of the embodiments of the invention.

It will be seen that with the apparatus according to the invention thelocal current density in the electrolyte and certain values correlatedwith the current density can be measured in such a manner that two probeelectrodes having a predetermined surface area and being spaced fromeach other a predetermined distance are immersed in the electrolyte at apoint where the current density is to be determined. Then theconductivity of the electrolyte is determined; the electrodes are sopositioned that the direct current in the electrolyte flows in directionfrom one to the other electrode so that now the potential diiferenceappearing between the electrodes can be measured whereby in view of theknown constants of the components of the apparatus the local currentdensity between the electrodes and certain other values dependingthereon become known.

The apparatus can be calibrated by applying it to an electrolyte ofknown conductivity in which case the latter does not have to bedetermined and the desired indication is obtained directly.

First, a preferred form of the probe means used in the apparatusaccording to the invention will be described in reference to FIG. 6. Ascan be seen, the probe means comprise a tubular member 3, open at bothends and preferably made of glass or some other non-conductive materialnot affected by the electrolyte, and two electrodes 1 and 2 made of awire mesh of platinum or socalled platinated platinum, also known asplatinum covered with platinum black, or Mohr platinum or spongyplatinum. The two electrodes are spaced from each other a fixed distanceand mounted parallel with each other and perpendicular to the axis ofthe member 3.

Referring now to FIG. 1, it can be seen that the general arrangement ofthe apparatus constitutes a Wheatstone bridge having four arms and adiagonal conductor circuit, resistors 4, 5, 6, 7, being connected inthree of the four branches in the manner shown, resistor 7 beingadjustable, preferably being of the potentiometer type having a slidabletap. The junction points between the four branches are marked A, B, C,and D. A source of alternating potential is connected to the junctionpoints A and C. A double-pole switch 8 is provided for conmeeting thebridge to said source whenever desired. The diagonal conductor circuitcomprises indicator means described further below connected between thejunction point D and the tap of the potentiometer 7. A switchover switch9 is connected with the junction point B and auxiliary conductors leadfrom the junction point D and from the above mentioned tap to thealternative contacts of the switch 9 so that the point B can bealternatively connected either with the point D or with said tap.Preferably, the contact arm of the switch 9 is mechanically coupled withthe arms of the switch 8' so that both these switches are movedsimultaneously between the position shown in full lines and the positionshown in dotted lines.

The diagonal circuit contains in series with an indicating instrument 12two potentiometers 10 and 11 connected in cascade so that the indicationof the instrument 12 can be influenced by adjustment of thepotentiometers .10 and/ or 11 so as to indicate a value adjustablyproportionate with a potential difference causing a response of theinstrument.

, A device S is further connected in series with the indicator means andwill be described further below.

The-apparatus operates as follows:

The probe means comprising the tube 3 and electrodes 1, 2 which areconnected in the fourth branch of the bridge between A and D is immersedin the electrolyte and the switch 8 is moved into its first positionshown in dotted lines whereby also switch 9 is moved into its firstposition shown in dotted lines. Now the instrument 12 will indicate apotential difference because it cannot be expected that the bridge A, B,C, D, is immediately in balanced condition. By moving the sliding tapalong the potentiometer 7 the bridge can be balanced. It is to be notedthat in this position of the switch 9 the portion of the branch A, Blocated between B and the tap is shunted so that the resistor 6 and aportion of the potentiometer 7 are ineffective. It is evident that afterbalancing the bridge the resistance (or conductance) between point A andthe tap is proportional to the resistance (or conductance) existing inthe electrolyte between the probes 1 and 2. If the resistors 4 and areequal then the just mentioned resistances or conductances are alsoequal. It can be seen that the adjustment of the potentiometer 7 isdirectly proportional with the conductivity of the electrolyte.

If now the switches 8 and 9 are moved into their second position shownin full lines, the supply of alternating voltage to the bridge isinterrupted and the junctions points B and D are directly connected witheach other whereby the resistors 4 and 5 in the branches B, C, D areshunted.

Now the probe electrodes 1 and 2 are immersed in the same electrolytewhich is passed by a direct current used for the electrolytic process.The tube 3 is to be oriented in such a manner that its axis points inthe direction of the flow of said current in the portion of theelectrolyte that is to be examined. It can be seen that now theinstrument 12 will indicate a potential difference. The magnitude ofthis potential difference is determined by the potential differenceappearing between the probe electrodes 1 and 2, subject to voltagedivision in accordance to the ratio of division existing at theresistors 6, 7 and at the potentiometers and 11.

Since the conductance between the point A and the tap as set along theresistor 7 during the preceding balancing of the bridge is proportionalwith the conductivity of the electrolyte, the conductance between theabove mentioned tap and the now directly connected points B, D will bethe larger, the smaller is the conductivity of the electrolyte.Consequently, the potential difference existing between the tap ofresistor 7 and the connected points B, D and applied to the instrument1?. via the potentiometers 10 and 111 will be the greater, the greateris the conductivity of the electrolyte. If the resistors 6 and 7 aresuitably dimensioned the potential diflerence just mentioned will bepractically proportional (within tolerances compatible with the purposeof the particular test) with the conductivity of the electrolyte. Now,since the potential difference between the probe electrodes 1 and 2 is,under the assumption of a given current density in the electrolyte,inversely proportional with the conductivity thereof, while the outputpotential of the voltage divider arrangement 6,7 is practicallyproportional to said conductivity, it follows that the output potentialof the voltage divider 6, 7 is an indication of the current densitywithin the tube 3 which indication is practically independent of theconductivity of the electrolyte. Therefore, the instrument .12 can becalibrated directly in terms of amperes per square inch as an indicationof current density.

In order to properly orient the tube 3 parallel with the direction ofthe current in the electrolyte at the particular spot the tube is to beturned until the indicating instrument 12 responds with the maximumdeflection of its pointer.

The potentiometers 1t and 111 are provided for the purpose of making itpossible to calibrate the instrument '12 in such a manner that if theapparatus is used in connection with a plating process, the instrumentwill directly indicate the amount of metal deposited per unit of time ona unit of surface area. The potentiometer 10 is to be adjusted in such amanner that the ratio between its output and input potential isproportional with the electro-chemical equivalent weight of the metal tobe deposited. For this purpose, the adjustment scale along thispotentiometer can be advantageously marked, instead of with figuresindicating the ratio of voltage division, with corresponding figuresindicating electricchemical equivalent weights. In addition, oralternatively, index markings may be applied corresponding to certainspecific metals. In particular, one point of that scale can bepredetermined by calculation on the basis of the output potential of thevoltage divider 6, 7 associated with a particular current density and onthe basis of the sensitivity of the instrument 12. Instead ofcalculating the position of said point, this point may also bedetermined empirically. The remaining points of the scale areautomatically determined by the dividing characteristic of thepotentiometer 10. Moreover, the potentiometer 10 may be adjusted so asto obtain an indication of the thickness of a deposit obtained during aunit of time, in which case the scale of this potentiometer wouldcontain suitable index marks provided with numerals and/or references toparticular metals. This adjustment of the potentiometer is done in sucha manner that the ratio between its output and input potentials isproportional with the electro-chemical equivalent of the metal to bedeposited and inversely proportional with the specific gravity thereof.The calibration of this scale can be performed again in a manner similarto the one set forth above taking into account the specificgravity ofthe metal to be deposited.

The potentiometer 11 functions in an analogous manher for taking intoaccount the cathodic efliciency.

If the apparatus is used in connection with electrolytic surfacemodification e.g. anodic oxidation or anodic polishing, thepotentiometer 10 may be provided with index marks associated with thesurface modifications of specific metals in which case the instrument 12is calibrated directly in units of time concerning the duration of theelectrolytic treatment. The calibration of the adjustment scale of thepotentiometer and of the instrument 12 may be carried out empirically.

Referring now to FIG. 2 which shows an embodiment generally identicalwith that of FIG. 1, it can be seen that the potentiometers 10 and 11are replaced by an amplifier device V including two amplificationcontrols 10' and 11' which may be used and adjusted exactly in the samemanner as the potentiometer 10 and 11, and calibrated analogously. Theamplifier V may be either of the electron tube or of the transistortype.

If the entire circuit is equipped with resister means of high ohmicvalues, the platinum electrodes can be dimensioned comparatively verysmall and the instrument 12 can be made highly sensitive, also in thecase of FIG. 2 sufficient amplification can be provided, so that arelatively small spacing of the probe electrodes will be sufiicient.Consequently, it will be possible to determine by means of the apparatusaccording to the invention the current density and correlated valueseven within very small areas and in connection with complicated surfaceformations. In this manner eg the amount of deposit per unit of time andthe required duration of an electrolytic process can be determinedsimply, rapidly and reliably under ordinary operating conditions.

The balancing of the bridge circuit is ordinarily carried out whiletemporarily the flow of current through the electrolyte is interrupted.However, it is also possible to carry out the balancing of the bridgewithout such an interruption of the current through the electrolyteprovided that the direct current component appearing between the probeelectrodes is prevented by a blocking device S connected in series withthe indicator instrument 1-2 as shown in FIG. 1 (provided the directcurrent in the electrolyte does not have substantial pulsations) fromentering the instrument 12. If, however, the direct current pulsatesconsiderably at a certain frequency, then the alternating voltageapplied to the bridge should have a frequency differing from thefrequency of said pulsation. In this case, the blocking device S wouldhave to be a filter device which prevents the pulsations of the directcurrent from entering the instrument 12. Of course, during thedetermination of the potential difference between the electrodes 1 and2, i.e. when the switches 8 and 9 are in their second position, a bypassswitch S must be closed in order to shunt the filter device.

As a material for the probe electrodes not only the above mentionedplatinum but also other material like graphite, antimony, gold, tantalumand other platinum metals e.g. rhodium may be used. Also, alloys of suchmetals are suitable. The electrodes do not have to be formed as a wiremesh but may also have the form of rings or pins.

Referring now to FIG. 3, which is generally based on the same concept asthe other embodiments of the invention, it can be seen that a variableresistor 7' is provided in the bridge branch A, B the resistance ofwhich is proportional with the conductivity of the electrolyte afterbalancing of the bridge, the control of the resistor 7' beingmechanically coupled, with a potentiometer 13 in such a manner that thedividing ratio between output voltage and input voltage is proportionalto the just mentioned resistance of the resistor 7 and therefore alsoproportional with the conductivity of the electrolyte. The potentiometer13 is connected in cascade with the previously described potentiometers10 and 11. A switch-over switch is provided between the electrodes 1, 2and the remaining parts of the arrangement.

Referring now to FIG. 4, a potentiometer 7" and a change-over switchcombination 8', 8" may be arranged in such a manner that thepartialresistance located between the tap marked C and one end of thepotentiometer 7" constitutes during the balancing of the bridge onebranch thereof the resistance of which is proportional with theconductivity of the electrolyte, while during the determination of thepotential difference at the probe electrodes 1, 2 these electrodes areconnected with both ends of the potentiometer '7" because in this casethe switch means 8, 8", are moved into their positions shown in dottedlines, so that the potential to be measured is that one which existsbetween the tap C' and the above mentioned end of the potentiometer 7".In this embodiment the dividing ratio of the potentiometer 7" isadjusted in the balancing of the bridge circuit in such a manner thatthe proportion between output and input potential is proportional withthe conductivity of the electrolyte. The potentiometer 7" is arranged incascade with the previously described potentiometers 10 and 11.

Referring now to FIG. 5, which is otherwise identical with that of FIG."1, amplifier means S are connected between the probe electrodes 1, 2and the bridge branch A, D. These amplifier means may consist of one ormore tube or transistor stages. In this case the various above mentionedvoltage divider means may also be replaced by amplification controlmeans. It is however advisable to use in direct connection with theprobe electrodes an. electron tube amplifier because this type ofamplifier is characterized by a large input resistance which is ofadvantage in this type of measuring potential differences with the aidof probe electrodes.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofapparatus for determining the density of a direct current flowingthrough an electrolyte differing from the types described above.

While the invention has been illustrated and dscribed as embodied inapparatus for determining the density of a direct current flowingthrough a particular portion of an electrolyte, it is not intended to belimited to the details shown, since various modifications and structuralchanges may be made Without departing in any way from the spirit of thepresent invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. Apparatus for determining the density of a direct current flowingthrough an electrolyte, comprising, in combination, a source ofalternating current; bridge circuit means connectable to said source andcomprising three bridge arms each including resistor means, at least oneof said resistor means being adjustable, a fourth bridge arm includingprobe means immersible in the electrolyte and including a pair of probeelectrodes spaced from each other for accommodating therebetween aportion of said electrolyte and enabling a current to flow directlythrough said portion of said electrolyte between said electrodes whenthe latter are immersed in said electrolyte, said electrodes having eacha predetermined surface area and being spaced from each other apredetermined distance, and diagonal conductor means including indicatormeans in circuit with said adjustable resistor means for indicating apotential difference appearing across said diagonal conductor means; andmeans for alternatively connecting said bridge circuit with said sourcefor determining the conductivity of said electrolyte by balancing saidbridge circuit through adjustment of said adjustable resistor means,and, on the other hand, for disconnecting said bridge circuit means fromsaid source and for altering the connections between said indicatormeans and said electrodes for determining the curent density betweensaid electrodes in spasms said electrolyte by determining the potentialdifference appearing between said electrodes as indicated by saidindicator means after said adjustment of said adjustable resistor meansfor determining said conductivity of said electrolyte 2. Apparatus asclaimed in claim 1 wherein said electrodes are made of platinum wiremesh and are mounted substantially parallel with each other.

3. Apparatus as claimed in claim 2 wherein said probe means comprise atubular member of non-conductive material open at both ends, saidelectrodes being mounted within said tubular member substantiallyperpendicular to its axis.

4. An apparatus as claimed in claim 1, wherein said one adjustableresistor is provided with adjusting means for adjusting the same forbalancing said bridge circuit means, and wherein said diagonal conductormeans comprise potentiometer means in circuit with said indicator means,said adjusting means being mechanically coupled with said potentiometermeans so that when said adjustable resistor is adjusted so as toestablish a balanced condition of said bridge circuit means determiningthe conductivity of said electrolyte, the adjusted ratio between inputand output voltage at said poentiometer is proportional to the specificconductivity of said electrolyte.

5. Apparatus for determining the density of a direct current passingthrough an electrolyte, comprising, in combination, a bridge circuitmeans comprising four bridge arms respectively connected by junctionpoints located between adjoining arms, and a diagonal conductor circuitconnecting two opposite first junction points and comprising indicatormeans for indicating a potential difference appearing between the endsof said diagonal conductor circuit; energy supplying circuit means forapplying an alternating voltage to the other two junction points;resistor means connected in three of said bridge arms, at least one ofsaid resistor means being adjustable for balancing said bridge circuitmeans; probe means including a pair of probe electrodes adapted to beimmersed in said electrolyte and connected in the fourth one of saidbridge arms, said electrodes having each a predetermined surface areaand being spaced from each other a predetermined distance foraccommodating therebetween a portion of said electrolyte and enabling acurrent to flow directly through said portion of said electrolytebetween said electrodes when the latter are immersed in saidelectrolyte; bypass means arranged for being connectable in parallelwith two of said bridge arms associated therewith for shunting thelatter; and switchover means connected with said bypass means andcomprising at least one first switch means connected in said energysupplying circuit means, and at least one second switch means connectedin said diagonal conductor circuit, both said switch means being movablebetween a first position in which said energy supply circuit and saiddiagonal conductor circuit are completed, respectively, for applyingsaid alternating voltage to said bridge circuit means and for connectingsaid indicator means operatively in said bridge circuit, while renderingsaid bypass means inoperative, and a second position in which saidsupply circuit and said diagonal conductor circuit are interrupted,while said bypass means are connected to shunt said bridge armsassociated therewith, whereby when said switch means are in said firstposition and said probe electrodes are immersed, the conductivity ofsaid electrolyte, after balancing said bridge circuit means by adjustingsaid adjustable resistor means, is indicated-by the amount of adjustmentof said adjustable resistor means, and when said switch means are insaid second position the current density between said electrodes in saidelectrolyte is indicated by the potential difference appearing betweensaid electrodes and indicated by said indicator means afterdetermination of said conductivity of said electrolyte by saidadjustment of said adjustable resistor means.

6. Apparatus as claimed in claim 5 wherein said probe 5: electrodes aremade of platinum wire mesh and are mounted substantially parallel witheach other.

7. Apparatus as claimed in claim 6 wherein a tubular member ofnon-conductive material open at both ends is provided for supportingsaid probe electrodes, the latter being mounted within said tubularmember substantially perpendicular to its axis.

8. Apparatus as claimed in claim 5 including amplifiers means having itsoutput terminals connected in the fourth one of said bridge arms, andhaving its input terminals connected with said probe electrodes.

9. Apparatus as claimed in claim 5 wherein said adjustable resistormeans is a potentiometer type resistor including a slidable top, andwherein said diagonal conductor circuit comprises one circuit portionconnected between one of said two opposite first junction points andsaid slidable top and including said indicator means, and two auxiliaryconductors, one of which serving as said bypass means for shunting thetwo bridge arms connected to said two opposite first junction points,the other one of said two auxiliary conductors serving as a shunt forthe bridge portion between said top and the other one of said oppositetwo first junction points. said second switch means being arrangedbetween said last mentioned junction points and the ends of saidauxiliary conductors for alternatively connecting said last mentionedjunction point with either one of said auxiliary conductors.

10. Apparatus as claimed in claim 9, wherein said indicator meanscomprise an indicating instrument and adjustment potentiometer means incircuit therewith for influencing the instrument indication so as toindicate a value adjustably proportionate with said potentialdilference.

11. An apparatus as claimed in claim 10, wherein said adjustmentpotentiometer means comprise a first and a second adjustmentpotentiometer connected in cascade.

12. An apparatus as claimed in claim 11, wherein condenser means areconnected in said diagonal conductor circuit in series with saidindicator means for preventing said direct current flowing between saidprobe electrodes from entering said indicator means during operation ofsaid apparatus while said switch means are in said first position.

13. Apparatus as claimed in claim 11 wherein filtering means areconnected in said diagonal conductor circuit in series with saidindicator means for preventing pulsations of said direct current at afrequency different from that of said alternating voltage, from enteringsaid indicator means during operation of said apparatus while saidswitch means are in said first position, and a switch device connectedin parallel with said filtering means for shunting the latter duringoperation of said apparatus while said switch means are in said secondposition.

14. An apparatus as claimed in claim 10, for use in connection withproducing electrolytic metal deposits on an object in said electrolyte,wherein said indicator means is calibrated to indicate the amount ofmetal deposited per unit of time on a unit of surface area of saidobject, and wherein said adjustment potentiometer means comprise afirst, second and third potentiometer means connected in cascade, saidfirst potentiometer means being adapted to adjust said potentialdifference across said diagonal circuit in accordance with theconductivity of said electrolyte, said second potentiometer means beingadapted to adjust said potential difference in proportion to theelectro-chemical equivalent weight of the metal being deposited, andsaid third potentiometer means being adapted to adjust said potentialdifference in proportion to the cathodic efficiency of said electrolyticprocess.

15. An apparatus as claimed in claim ,14, wherein at least one of saidpotentiometer means is provided with a calibration and index means forsetting the same thereby so as to produce the desired respectivepotential difference.

16. Apparatus as claimed in claim 10, for use in connection withproducing electrolytic metal deposits on an object in said electrolyte,wherein said indicator means is calibrated to indicate the thickness ofa metal layer deposited per unit of time on a surface area of saidobject, and wherein said adjustment potentiometer means comprise afirst, second and third potentiometer means connected in cascade, saidfirst potentiometer means being adapted to adjust said potentialdifference across said diagonal circuit in accordance with theconductivity of said electrolyte, said second potentiometer means beingadapted to adjust said potential difference in proportion to the ratiobetween the electro-chemical equivalent weight of the metal beingdeposited, and the specific gravity of said metal being deposited andsaid third potentiometer means being adapted to adjust said potentialdifference in proportion to the cathodic efiiciency of said electrolyticprocess.

17. An apparatus as claimed in claim for use in con nection with aprocess for electrolytically modifying the surface of an object in saidelectrolyte, wherein said indicator means is calibrated to indicatedirectly the time required to produce under given conditions the desiredsurface modification, and wherein said adjustment potentiometer meanscomprise a plurality of potentiometer means connected in cascade, afirst potentiometer means thereof being adapted to adjust said potentialdifference in accordance with the conductivity of said electrolyte, andother potentiometer means of said plurality thereof being adapted toadjust said potential difference in accordance with the type of saidsurface modification, with the type of material the surface of which isto be modified, with the type of electrolyte being used, and with thecathodic efficiency of said electrolytic process.

18. Apparatus as claimed in claim 9, wherein said indicator meanscomprise an indicati g instrument and amplifier means in circuittherewith, said amplifier means including amplification control meansfor influencing the instrument indication so as to indicate a valueadjustably proportionate with said potential difierence.

19. An apparatus as claimed in claim 18 for use in connection withproducing electrolytic metal deposits on an object in said electrolyte,wherein said amplification control means comprise a first, a second anda third amplification control device, each provided with a calibrationand index means for adjusting thereby the respective control device inaccordance with the conductivity of said electrolyte, wtih theelectro-chemical equivalent Weight of the metal being deposited, andwith the cathodic efliciency of said electrolytic process, respectively.

20. An apparatus as claimed in claim 18, for use in connection withproducing electrolytic metal deposits on an object in said electrolyte,wherein said amplification control means comprise a first, a second anda third amplification control device, each provided with a calibrationand 1t index means for adjusting thereby the respective control devicein accordance with the conductivity of said electrolyte, with the ratiobetween the electrochemical equivalent weight of the metal beingdeposited and the specific gravity thereof, and with the cathodicefficiency of said elecrolytic process, respectivly.

21. Apparatus for determining the density of a direct current flowingthrough an electrolyte, comprising, in combination, a source ofalternating current; bridge circuit means connectable to said source andcomprising three bridge arms each including resistor means the resistormeans of two of said arms being of the potentiometer type having aslidable tap member constituting the junction point between said twoarms so that the portions of said potentiometer on opposite sides of thevariable position of said tap member constitute the resistor means insaid two arms, a fourth bridge arm including probe means comprising apair of probe electrodes adapted to be immersed in said electrolyte,said electrodes having each a predetermined surface area and beingspaced from each other a predetermined distance for accommodatingtherebetween a portion of said electrolyte and enabling a current toflow directly through said portion of said electrolyte between saidelectrodes when the latter are immersed in said electrolyte, anddiagonal conductor means including indicator means in circuit with saidadjustable resistor means for indicating a potential differenceappearing across said diagonal conductor means; and means foralternatively connecting said bridge circuit with said source fordetermining the conductivity of said electrolyte by balancing saidbridge circuit through adjustment of said potentiometer type resistormeans, and, on the other hand, for disconnecting said bridge circuitmeans from said source and for shunting the resistor means in the thirdone of said bridge arms and for connecting said tap member with saidindicator means, thereby altering the connections between said indicatormeans and said electrodes for determining the current density betweensaid electrodes in said electrolyte by determining the potentialdifference appearing between said electrodes as indicated by saidindicator means after said adjustment of said adjustable resistor meansfor determining said conductivity of said electrolyte.

References Cited in the file of this patent UNITED STATES PATENTS

